The present invention relates to an improved construction for electrically actuated globe control valves used, for example in water based heating and cooling systems for buildings.
Generally speaking, fluid control valves for such heating and cooling systems evolved from pneumatically driven valves, and therefore, most engineering and pressure calculations evolve from the application of pneumatic actuators opposing springs and of course the valve stem and valve plug. A pneumatic actuator works only in one direction. Air pressure opposes the force of the valve plug against the seat and an additional spring is added both to oppose the actuator when there is no differential pressure across the valve, and also to bias the valve so that the valve will work within the operating range of the pneumatic controller. When electric actuators were added to the valves to replace pneumatic ones, that thinking, (the force calculations, etc., along with the spring, etc.), was forgotten since the electric actuators work in both directions.
When electric and electronic actuators are applied, they have the ability to apply equal force in either direction. They are also usually much more expensive than their pneumatic counterparts. As the industry applies them conventionally, they work hard to close the globe valve plug against its seat and the differential pressure of the fluid. In the return direction, the motors do virtually no work. In fact, they are pushed off the seat by the differential force of the fluid against the plug. Clearly, half the work is being wasted.
One current and common approach towards attaining improved close-off differential pressures is to apply a xe2x80x9cbalancedxe2x80x9d globe valve, but such valves are expensive to produce and have an inherent minimal leakage factor often undesirable and wasteful of energy in the closed position. These valves, xe2x80x9cdouble seated valvesxe2x80x9d, have two plugs and two seats, one set closing with the pressure and one set closing against the pressure. Accordingly, they are also expensive. Another type has a hole from beneath the seat to above a piston at the top of the valve, to push down the seat with a force equal to the upward force. These valves are susceptible to dirt and shavings, and seals which wear and leak.
It is an object of the present invention to provide a construction which will improve the close-off pressures of electrically and electronically motorized globe valves.
In accordance with the present invention there is provided a globe valve system for controlling the flow of fluid in a pipe, the system comprising a pipe-receiving body having within it a fluid passage, a valve seat and a globe valve plug movable between an open position allowing fluid flow through the passage and seat and a closed position blocking said fluid flow. Means are provided to move the valve plug between open and closed position. A biasing means is also provided, to assist the valve plug in moving from open to close position.
In a preferred embodiment of the present invention, the biasing means comprises a compression spring, the force of which balances the force against the valve plug as it closes.
By providing a bias which offsets the force operating against the actuator as it closes the valve, the close off pressure can be doubled (less the spring rate and the valve friction). In this case, the actuator will have to work in both directions, to compress the compression spring as the valve is opened, and to close the valve.